Hmm. I'm not sure which pin is referred to as "AUX". However, it is possible that this is the pin also referred to as "12 volts" (as mentioned by Mud Dog) or "battery charge". In this case the pump should have worked. However, several of our members have reported that their Chevy tow vehicle came from the factory with no fuse inserted in this line, and hence no charge current flows to the trailer battery. This might be what you are experiencing. Check this out using the fuse locater in your Chevy owner's manual.
Bill
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